1. Field of the Invention
The present invention relates to a substrate transfer device.
2. Description of the Related Art
Substrates such as the semiconductor wafers are carried by holders such as the wafer cassette and wafer carrier in the course of manufacturing semiconductor devices. These holders for holding substrates to be carried are made by light and cheap resin and designed to house 25 sheets of semiconductor wafers, for example.
In a case where a plurality of the semiconductor wafers are batch-processed in a heat processing apparatus, for example, the above-mentioned resin-made holders cannot be used. A holder for holding substrates to be processed which is called wafer boat made of quartz excellent in chemical stability and heat proofness is therefore often used. This holder is designed to house over a hundred sheets of semiconductor wafers.
A substrate transfer device disclosed in Japanese Patent Disclosures Sho 60-231337 and 61-54639 is used to transfer the semiconductor wafers between the wafer boat and the wafer cassettes. The substrate transfer device supports the wafer boat substantially horizontal, grasps plural sheets of semiconductor wafers in the wafer cassettes and then transfer them to the wafer boat.
In a case where the semiconductor wafers are processed in the vertical heat processing apparatus, however, dummy wafers are arranged on the top and bottom of the semiconductor wafers to be processed and a test wafer is arranged every predetermined number of the semiconductor wafers to be processed. When plural sheets of the semiconductor wafers are grasped and transferred as a unit as described above in this case, the dummy wafers which are not to be processed are carried together into the vertical heat processing apparatus. In the case of another substrate transfer device intended to transfer the semiconductor wafers one by one, it takes a long time to transfer the wafers.